Which manhwa

I’m trying so hard to remember the name of it but I can’t but it’s a bl where the mc helps the ml go to sleep, mc has brown hair and eyes and has a cat and it’s historical and mc came from another world, was overworked, and now writes letters to the ml and other ppl for others. ml is blonde and has like a disguise, when he goes to sleep he wears a goofy ass outfit. Ughh it was so good I need to know the name